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Triassic - Jurassic Geology of the Southern Part
of the Culpeper Basin and the Barboursvllle Basin f
VIrglnia
by
K. Y. Lee
U.S. Geological Survey
Open - file Report 80 - 468
TRIASSIC-JURASSIC GEOLOGY OF THE SOUTHERN PART
OF THE CULPEPER BASIN AND THE BARBOURSVILLE BASIN,
VIRGINIA
by
K. Y. Lee
Regional setting and previous investigations
The Culpeper and Barboursvilie basins are north-northeast trending
faulted Mesozoic troughs bordering the east front of the /Appalachian
Mountains in Maryland and Virginia. These basins were initially evolved
during the early Mesozoic period of continental fragmentation that
preceded continental drifting and the development ofthe modern Atlantic
continental margin (Van Houten, 1977 f p. 83 and 89~96). The basins
are part of a belt of similar faulted Triassic-Jurassic troughs in the
Piedmont Province of eastern North America. The Culpeper basin, the
larger of the two troughs (fig. 1) 9 is about 20 km wide and extends for
li*0 km, whereas the Barboursvilie basin to the south (herein named
after the town of Barboursvilie, Va.) is a detached outlier (Conley
and Johnson, 1975) about k km wide and 16 km long. The 18 partial
2geologic maps (1:2*4,000) presented here cover about 1,690 km (fig. 1).
Figure 1 near here
Redfield (1856, p. 357) first designated W. B. Rogers 1 "New Red
Sandstone of the Atlantic slope" in Virginia as the Newark Group:
subsequently these rocks were redefined by I. C. Russel in 1879.
Norn., of QU odronoU.»nlhl. -port ,
I.ThorougMort Gop Z.WorrenfO* - S.Coilell 4.1nd«p.nd.nl HJll .
S.Brondy Sloiloft 6.Ritn1nglo»
7.M!dlond B.Scmtrrlllt 9.Jef\*9
lO.Culpeper Wttl M.Cu1ptp«r Cosl
IZ.G.rmonno Brldgt 13. RIct.ord.»!II«
|4.Wcd!»on Mill! IS.Rcpidon
le.Unlonvillt l7.Borfcoyr»»Illt
j&.6ordon»rllU
»7*30
PublUhtd b
.t. Lte.i»7t
71/2
Topogrophic Quodrongle Mop•^
1 7»M6* \
10 Mll«i
ft 10 tc;i»M»t»rt
Figure I.Index Mop Showing Geologic Mops, I « 24.0OO, In the
Southern Port of Culpeper Bosln ond Borbouriville Botln, Virginia
Roberts (1922, 1923, 1928) carried out the first detailed study of the
Triassic geology of Virginia and subdivided the Trlassie rocks of the
basins into the Manassas Sandstone and the Bull Run Shale. Cornet
(1977) established the presence of Lower Jurassic rocks in these basins
and the position of the Triassic-Jurassic boundary based upon a detailed
palynostratigraphic study. Lee (1977) presented a revised stratigraphy
for the northern part of the Culpeper basin on the basis of lithologic
sequences and depositional environments. Lee (1979) utilized ant.
informal stratlgraphic nomenclature for the rocks of the Culpeper basin
to present the 16 partial geologic quadrangle maps in the northern part
of the Culpeper basin. r<
Stratigraphy and structure
Triassic and Jurassic siltstone, sandstone, conglomerate, and
shale comprise the Culpeper and Barboursville basins. Jurassic basalt
and diabase are exposed in the Culpeper basin only. The sedimentary
rocks constitute a distinctive sequence of continental red beds
consisting of clastic fluvial and lacustrine deposits.
The informal stratlgraphic nomenclature of Lee (1979) is also used
in this report. The Culpeper Group is used herein for the Upper
Triassic and Lower Jurassic sedimentary and basaltic rocks within the
Culpeper and Barboursville basins. The sequence is subdivided, in
ascending order, into the Manassas Formation, the Balls Bluff Siltstone,
and the Bull Run Formation. The Upper Triassic Manassas Formation
contains the Reston Member and the Rapidan Member at its base which
both grade upward into and intertongue with the Poolesvilie Member.
The fine-grained deposits of the Upper Triassic Balls Siltstone
locally are gradational or intertongue with the coarser-grained
deposits of the Manassas below and the Bull Run above. The Lower
Jurassic Bull Run Formation consists of the Catharpin Creek Member,
which is conformably overlain by and intertongues with the Mountain Run
Member. The Catharpin Creek Member contains the Mt. Zion Church basalt,
the Hickory Grove basalt, and the Sander basalt. The rocks of the
Culpeper Group in these basins are locally mantled by unconsolidated
upper Tertiary (?) and Quaternary terrace deposits and colluvial
mountain-wash deposits, and Holocene alluvial deposits.r -s
During the latest stage of Bull Run sedimentations the sedimentary
rocks and basaltic flows within the basins were tilted toward the west
and northwest. The tilting was accomplished by renewed movement along
the border faults, particularly the western border faults of the
Culpeper basin, that was synkinematic with the development of minor
folds and shallow faults in rocks within the basins and with extensive
intrusion of tholeiitic diabase sills, stocks, and dikes that caused
thermal metamorphism of the country rocks. This metamorphism was
accompanied locally by sulfide and iron mineralization, hydrothermal
alteration, and zeolite mineralization in fissures of the contact
aureoles, the diabase, and host rocks outside the aureoles.
Economic Geology
The southern part of the Culpeper basin and the Barboursvi11e
basin contain significant groundwater reserves and extensive deposits
of rock materials suitable for crushed stone, aggregate, road metal,
and riprap, as well as deposits used for dimension stone and monumental
stone. Raw materials suitable for manufacture of brick and tile are
also abundant. Metal.lic and non-metallic material deposits have been
extensively prospected in the past, but were mined only or> a small
scale.
Supplies of groundwater adequate for domestic purposes are
available in most areas underlain by the sedimentary forks, and
potential supplies sufficient for commercial uses are likely In somes • *
of these areas. Water from the Balls Bluff Siltstone is more likely
to have high concentrations of calcium, magnesium, and sulfate than
water from other sedimentary units (A.J, Froelich, 1979 t Pers. commun.).
Basalt is locally quarried for crushed stone, aggregate, road
metal, fill, subbase, and riprap at the Sander quarry in the Catlett
quadrangle and at the Silver Lake quarry in the Thoroughfare Gap
quadrangle. Diabase has been quarried for dimension stone at the
Virginia Granite Company quarry and for monumental stone at the Aston
quarry In the Rapidan quadrangle. The diabase in these areas is
generally easily quarried due to its equigranular texture and an
intersecting network of widely spaced joints which facilitate splitting.
The Balls Bluff Siltstone 1s quarried for crushed stone,
aggregate, road metal, fill, and subbase at the Culpeper Crushed Stone
quarry in the Culpeper East quadrangle. It has also been quarried for
the manufacture of red brick and tile at the Webster Brick Company
quarry in the Gordonsville quadrangle. Resistant sandstone of the
Catharpin Creek Member was formerly quarried for dimension stone south
of U.S. Route 23/211 in the Thoroughfare Gap quadrangle.
Metallic copper and iron mineral deposits in the Culpeper basin
were prospected and locally mined on a small scale during the past.
These deposits generally occur in granulite and hornfel? of the inner
zone of contact aureoles, within fractures in diabase, and as fissure
fillings in sandstone and siltstone outside the contact aureoles.r •
Principal minerals are chalcopyrite, magnetite, specu^arite, bornite,
and malachite. Non-metallic barite deposits occur typically as
fissure fillings locally in siltstone and shale near diabase intrusives
Potential environmental problems within the basins are related to
waste disposal and to contamination of groundwater by septic tank
effluent or landfill leachate. Other problems relate to foundation
instability caused by highly expandable clays in soils developed on
diabase and basalt or within fault gouge, and by the settlement or
failure of unconsolidated colluvial deposits along the basin borders.
REFERENCES CITED
Conley, J,F., and Johnson, S»S t| 1975, Road log of the geology froft
Madison to Cumberland Counties in the Piedmont, central Vtrghilaj
Virginia Minerals, v, 21, n, k, p, 29^39t *
Cornet, Bruce, 1977» The palynostratigraphy and age of the Newark
Supergroup: University Park, Pa,, The Pennsylvania State University,
unpublished Ph.D, dissertation, 505 p*t-
Eggleton, R,E,, 1975, Preliminary geologic map of the Herndon quadrangle,
Virginia: U,S, Geological Survey Opem-file report 75 * 386, scale
1:24,000. r •
Lee, K,Y., 1977, Triasstc stratigraphy in the northern part of the
Culpeper bastn, Virginia and Marylandi U*S t Geological Survey
Bulletin 1422 * C f 17 p*
Lee, K.Y\, 1978, Geologic map of the Arcola quadrangle, Virginia:
U,S, Geological Survey Map MF ^ 973, scale Ij2^,000
Lee, K.Y., 1979, Triassic-Jurassic geology of the northern part of the
Culpeper basin, Virginia and Maryland: U,S, Geological Survey Open*
file report 79 - 1557, 16 partial geologic maps, scale 1;2^,000,
Redfield, W.C., 1856, On the relations of the fossil fishes of the
sandstone of Connecticut and other Atlantic States to the Liassic and
Jurassic periods: American Journal of Science, v. 22, ser. 2,
p. 357 - 363-
Roberts, J.K., 1922, The Triassic of northern Virginia: Baltimore,
Maryland, Johns Hopkins University, unpublished Ph.D, dissertation,
272 p.
Roberts, J.Kt , 1923, Trlasstc bsslns of northern Ytrgtntot
Geologist, v. 29, n, 3, p» 185 * 20Q %
Roberts, J,K,, 1928, The geology of the Virginia Triassic; Virginia
Geological Survey Bulletin 29 f 205 p*
Van Houten, F,B,, 1977 f Triassic^Liassic deposits of Morocco and
Eastern North America; comparison; American Association of
Petroleum Geologists Bulletin, v. 61, n t 1, p, 79 ^ 99-
——..... Contact, approximately located; short dashed where inferred;
dotted where concealed.
•——•- Fault, approximately located; bar and ball on downthrown
side; short dashed where inferred; dotted where concealed.
2V V Strike and dip of beds
© Horizontal beds
J 50°Q__ Strike and dip of overturned beds
L 61°r Strike and dip of principal metamorphic foliation
| Strike of vertical metamorphic foliation
Minor fold~showtng plunge
Anticline
SynclIne
Strike and dip of joints. In case of multiple joints, point
of observation is at Intersection of symbols.
70°Inclined
Vertical
8
Direction of paleocurrent; measurement at apex based on
cross lamination of sandstone and imbricate structure of
rock fragments in conglomerate.
Quarry, Mine or Prospect
Active
AA Abandoned. Cu-Copper, Ba-Barite
Q Fossil locality
Qal
Qmw
QTg
DESCRIPTION OF MAP UNITS
Artificial fill and stripped land surface. Hanmade
features in construction areas.
UnconsolJdated Sediments
Alluvium - Silt, sand, clay, and gravel; generally moder
ately well-sorted. Commonly, sand layers contain gravel
lenses chiefly composed of pebbles of rounded to subrounded
rock fragments. Locally contains residual manganese and
iron nodules In the Thoroughfare Gap and Rapidan quadrangles, r •
Estimated to be 0.5 to more than 8 m thick*
Mountain Wash - Gravel, silt, and sand; gray and moderate-
redd ish^-brown to pale-yellowish-orange; chiefly rounded to
angular quartzite and vein-quartz clasts with locally
abundant greenstone, sandstone, and schist fragments, and
light-gray to gray and moderate-reddish-brown quartz and
feldspar sand In a silt matrix. Estimated to be 0.1* to more
than 30 m thick. Not mapped where underlain by pre-Triasslc
rocks.
Terrace Deposits ~ Sand, gravel, and clay; gray, grayish-
orange, and moderate^reddish-brown; chiefly rounded to sub-
rounded quartzite, vein-quartz, schist, and greenstone
fragments with locally abundant quartz and feldspar sand in
a clayey silt matrix. Estimated to be 1 to about 10 m thick.
Not mapped where underlain by pre-Trlassic rocks.
Thermally Metamorphosed Rocks
Hornfels, granulite, and quartzite ~ Gray to dark-gray,
medium-blulsh-gray, and olive-black; chiefly metamorphosed,
feldspathic, micaceous, argillaceous, ferruginous, and
calcareous sandstone, siltstone, and shale; includes
slightly thermally altered basalt, Hornfels is the dominant
type of metamorphosed argillaceous rock. Granulite andt
quartzite form fused lenses, bands, and irregular masses.
Principal metamorphic mineral assemblages are cordierite,
andalusite, quartz, plagioclase, epldote tr bjotite, and<
chlorite.
intrusive Rocks
Diabase - Medium- and medium-dark-gray; chiefly equigranular
and medium-grained, but locally very coarse-grained,
aphanitic near chilled margins; consists chiefly of dark-
grayish-green to black discrete crystals of augite and
pigeonfte, light-gray labradorite and Slmenite. Pegmatittc
diabase and granophyre (JTrdp) occur as locally mapped
irregular pods and bands within the diabase. Granophyre
(JTrdg) - Pale-pink to pink, medium^ to coarse-grained;
consists chiefly of sodic plagioclase with a turbid appear*
ance, mlcropegmatltic quartz, and potassium feldspar
associated with discrete crystals of hornblende and clino-
pyroxene and minor biotlte, actinolite, magnetite, ilmenite,
chlorite, and apatite.
JTrbcs
Sedimentary Rocks and Basalt of the Culpeper Group
BULL RUN FORMATION
MOUNTAIN RUN MEMBER - Conglomerate, dusky-yellowish, dusky-
grayish-, and moderate-yellowish-green; chiefly angular to
• . subrounded clasts of greenstone with subordinate rounded
to subrounded clasts of quartzite and feldspathic sandstone
and locally abundant sandstone, vein-quartz and minor schist
In a clayey sand and silt matrix, firmly cementecj by silica.
Estimated to be 150 to 635 m thick.
CATHARPIN CREEK MEMBER - Sandstone, siltstone, and minor
conglomerate and shale, grayish-red and dusky-red mostly
in the lower part of the sequence; light-brown, pale-yellow-* • •»
ish-brown, and moderate-yellowish-brown In the upper part,
tnterlayered, in part, with basalt flows; locally contains
fossi1iferous (fish fossils) impure limestone, carbonaceous
shale and siltstone, and sandy siltstone containing
dinosaur tracks. Estimated to be *»0 to about 5,150 m thick.
SANDER BASALT -• Basalt, dark-gray to blackish- or bluish*
gray; mostly holocrystalline and equigranular, in part
microcrystalline or glassy and porphyritic; consists of
augite and plagioclase, chiefly labradorite and andesine,
in part exhibiting ophitic texture. Zeolite-filled
vesciles are common in the upper part of the unit,
Hydrothermally altered and locally mineralized with copper
sulfi.de minerals, Interlayered with sandstone and siltstone
of the Catharptn Creek Member. This basalt is truncated by
western border faults but part of the unit, apparently thins
and pinches out near the southwestern border of the Remington
quadrangle and the eastern border of the Brandy Station
* .quadrangle. Estimated to be as much as 5^5 m thick.
HICKORY GROVE BASALT - Basalt, medium-gray to medium-dark-
gray; very fine to very coarse-grained; mostly equigranular
and holocrystalline; euhedral or subhedral crystals of
plagioclase, chiefly labradorite and andesine, occur in a
groundmass of auglte. Vesicles mainly in the upper part of* r « the unit. This basalt apparently pinches out tjear the
southwestern border of the Remington quadrangle. Estimated
to be as much as 210 m thick.
MOUNT ZION CHURCH BASALT 7 Basalt, medium-gray and dark-gray;
very fine- to medium-grained, porphyritic in part; mostly
equigranular and holocrystalline; augite and plagioclase,
chiefly labradorite and andesine, display ophltic or
subophitic texture. Vesicles generally occur in the upper
part of the unit. Columnar joints are well developed.
Exposed only as Isolated, narrow outcrops in the Catlett
and Remington quadrangles. Estimated to be as much as 100 m
thick.
BALLS BLUFF SILTSTONE
SILTSTONE - Dusky-red, dark-red, grayish-red, and In part,
1ight-greenish-gray, 1ight-blulsh-gray, greenish-gray, and
medlum-dary-gray to dark-gray; feldspathic, micaceous,
highly calcareous, ferruginous, and argillaceous; thin- to
thick-bedded or massive; ripple-bedded and laminated.
Locally contains thin to thick lenses of gray limestonet
and dolomite, layers and lenses of carbonate ooids,
aggregates of carbonate concretions, and dinosaur tracks.
Layers of sandstone and sllty shale are .scattered throughout*
the sequence. Estimated to be 10 to 1,630 m thick.
MANASSAS FORMATION ..
POOLESVILLE MEMBER - Sandstone, dusky-red to grayish-red
and very dark-red; very fine- to medium-grained, mostly
medium-grained; micaceous, feldspathic, ferruginous, silty,
clayey, and in part calcareous; consists chiefly of quartz
and feldspar grains in silt matrix, cemented by clay,
silica, and locally calcite. Thick- to very thick-bedded
or massive; planar- to cross-bedded. In the lower part of
the sequence, contains lenses and layers of light-gray to
gray, medium to very coarse-grained, feldspathic sandstone
and conglomerate composed of quartz!te and vein-quartz
fragments. Estimated to be 50 to *»60 m thick.
Trmra RAP I DAN MEMBER - Conglomerate, grayish-green, dusky^green,
and grayish-olive-green; angular to subrounded clasts of
greenstone and minor amounts of gray quartzite, vein-quartz,
and feldspathic sandstone. These clasts are in a clayey
sand and silt matrix, firmly cemented by silica. Estimated
to be 70 to 140 m thick.
RESIGN MEMBER «• Conglomerate and sandstone, generally
loosely coherent near the surface; consists of abundant to
sparse, angular to subangular, pebble- to cobble-sized
clasts of greenish-gray mica schist, light-gray to gray
rounded to subrounded quartzite, vein-quartz, and feld
spathic sandstone tn a dusky-red, dark-red, very dusky-red-
purple, and moderate-brown matrix of clay and silt- and
sajnd-sized quartz and feldspar. Sandstone, dusky-red,
dark-red, and very dusky-red-purple; medium* to very
coarse-grained; generally loose to semi "-compact near the
surface; micaceous, ferruginous, silty, and clayey; consists\
chiefly of feldspar and quartz grains in a silt matrix;
locally massive and cross-laminated. Estimated to be 3 to
about 100 m thick.
Pre-Triassic CrystalHne Rocks —
Undifferentfated pre-Triassic crystalline rocks,
SCHIST - Medium- to dark-gray and grayish-green; medium- to*
coarse-grained; consists chiefly of mica, quartz, chlorite,
and plagioclase. Intensely foliated with alternating quartz-
and mica-rich laminae that are crossed by strain-slip
foliation. Locally cut by quartz veins. r
GREENSTONE - Dusky-yellowish-, dusky-grayish-, and moderate-
yellowish-green, and graylsh-ollve-green, metamorphosed
igneous and sedimentary rocks; epidotizattoo and chlorjti-<
zation common; generally intensely foliated.
SANDSTONE AND QUARTZITE'- Light-gray, light-brown, grayish-
red, and dusky-red; fine- to very coarse-grained; feldspathic,
micaceous, and ferruginous; thick- to very thick-bedded and
very compact; generally intensely foliated. Locally cut by
intersecting networks of quartz veins.
V Contacts between pre-Triassic and Triassic or Jurassic
rocks are Inferred where covered by Qmw or QTg.